1. Field of the Invention
This invention relates to apparatus for detecting flaws on metal materials, and particularly to those with probes which are revolved around a bar of metal material so as to detect flaws on its circumference while the material is passed through the apparatus in its lengthwise direction.
2. Description of the Prior Art
When the foregoing technique is used to detect flaws, the probes are required to keep a constant distance from the circumference of the material, while revolving around the material, in order to ensure a higher degree of detection accuracy.
With reference to FIG. 17, the conventional detector of the type stated comprises a circular means 303 which is rotatable around a predetermined axis 302 of a material 301 to be passed through the detector and a cylinder 304 which is connected to the rotator means 303 and has a piston rod 304a provided with a probe 305 at its one end. In addition, the probe 305 is provided with a sensor means 306 which determines the distance between the probe 305 and the material 301. In such a constrction, if the material 301 happens to deviate from its predetermined axis 302 while passing the detector, the amount of deviation is detected by the sensor means 306 and the probe 305 is displaced by the cylinder 304 according to the detected amount of deviation so that the probe 305 keeps the unvaried distance from the material 301. To be more exact, the actual axis of the material may deviate from its predetermined one 302, or the rotational center of the rotator means 303, as indicated by numeral 307 (if the material is warped at a certain portion thereof) so that the material comes to the position indicated by a dot-dash-line; thereupon, in order to keep the constant distance, the probe 305 is withdrawn the same distance as the deviation of the material axis (the deviation distance hereafter called "L") while the probe 305 revolves 180.degree. (immediately after the deviation has occurred), and then advanced the distance L while it revolves another 180.degree.. That is, after the material axis has deviated, the probe 305 is removed by twice the distance L while it makes one revolution. In addition, the rotator means 303 may be rotated, for example, at a rate of several tens of revolutions per second; where such is the case, therefore, the probe 305 is required to keep reciprocating at an extremely-high velocity so as to cover the entire range of continuous deviation of the material axis, thus calling for an extremely-excellent degree of technique therefor.